Current work in synthetic biology is focused on modifying protein structure and function, and regulation of gene expression circuits at the level of transcription promoters (Kwok, 2010). While promoter control of expression may be sufficiently specific in bacterial systems, heterologous promoters confer only limited control of gene expression (e.g. cell-specific expression) in eukaryotic cells, possibly because of a lack of correct chromatin assembly (Wolffe, 1999). The limited control of gene expression in eukaryotic cells by heterologous promoters alone may be insufficient for certain therapies and other biotechnological applications. Complete spatiotemporal control of gene expression is important for the use of at least a subset of biological molecules in gene therapy and other biotechnological applications.